The present invention relates to a mercury-free high-intensity discharge lamp operating apparatus and a mercury-free metal halide lamp that do not contain mercury as the luminous material.
In recent years, high-intensity discharge lamps for general lighting, projectors and vehicle headlights are being used. High-intensity discharge lamps have advantages of high efficiency, low power consumption, and brightness, compared with halogen lamps, so that the high-intensity discharge lamps are expected to be widely used. One of the high-intensity discharge lamps that are expected to be widely used is a metal halide lamp. FIG. 1 shows a cross sectional configuration of a metal halide lamp.
The metal halide lamp shown in FIG. 1 includes an arc tube (luminous bulb) 1 made of quartz glass and sealing portions 2 that are positioned at both ends of the arc tube 1 and seal the arc tube 1. A pair of electrodes 3 made of tungsten are provided in the arc tube 1, and a luminous material 6 including mercury and metal halide, and a rare gas (not shown) are enclosed in the arc tube 1. The pair of electrodes 3 in the arc tube 1 are connected to molybdenum foils 4 at one end, and the molybdenum foils 4 are sealed with the sealing portions 2. Lead wires 5 are connected to the other ends of the molybdenum foils 4. The lead wires 5 are to be electrically connected to a ballast (not shown).
The principle of light emission of the metal halide lamp shown in FIG. 1 will be described briefly. When the lamp is turned on by applying a voltage to the lead wires 5 from the ballast, a part of or the entire metal halide 6 evaporates. Then, the evaporated metal halide is dissociated to metal atoms and halogen atoms by arc discharge occurring between the pair of electrodes 3, and thus the metal atoms are excited so that light is emitted. In the vicinity of the wall of the arc tube 1, the dissociated metal atoms are recombined with the halogen atoms, and return to a metal halide. This cycle phenomenon is repeated to allow the lamp to be stably on. In general, although the metal halide has a lower vapor pressure than that of mercury, the metal halide is readily excited and emitted, so that there is a tendency that emission caused by an added metal mercury is stronger than emission caused by mercury in metal halide lamps. Therefore, mercury primarily serves as a buffering gas to determine a voltage in the arc tube 1. A rare gas in the arc tube 1 serves as a gas for starting the lamp.
In general high-intensity discharge lamps including the metal halide lamp shown in FIG. 1, the lamp is operated while the straight line connecting the pair of electrodes 3 is horizontal (hereinafter, referred to as xe2x80x9chorizontal operationxe2x80x9d), an arc 7 occurring between the pair of electrodes is curved upward by convection current of the vapor in the arc tube 1, as shown in FIG. 2. When the degree of curving is large and the arc 7 is attached to the wall of the arc tube 1, the temperature to the upper portion la of the arc tube 1 is locally high, so that devitrification or deformations of the upper portion 1a of the arc tube start comparatively in an early stage. As a result, the lifetime characteristics of the lamp are degraded.
In order to suppress the curving of the arc 7 to improve the lifetime characteristics of the lamp, there are several proposals. One of them is a technique of applying a magnetic field to a metal halide lamp to suppress the curving of the arc, which is disclosed, for example, in Japanese Laid-Open Patent Publication Nos. 55-86062 and 9-161725. The technique disclosed in Japanese Laid-open Patent Publication No. 55-86062 includes the step of disposing a strong rare earth magnet above the arc tube 1 in a metal halide lamp containing mercury in the arc tube 1 to lower the arc 7 down by utilizing repulsion (Lorentz force) between the magnet and the arc 7, thereby suppressing the curving of the arc 7. On the other hand, the technique disclosed in Japanese Laid-open Patent Publication No. 9-161725 uses an electromagnet as means for applying a magnetic field, in place of the rare earth magnet. There are other disclosures of the technique of utilizing an electromagnetic to change the position of the arc, such as Japanese Laid-Open Patent Publication No. 11-312495, 11-317103, and 2000-12251.
Nowadays, environment is an important issue, and metal halide lamps not containing mercury are desirable in view of environmental issues arising when disposing of waste. Therefore, the inventors of the present invention compared and examined mercury-free metal halide lamps and metal halide lamps containing mercury to develop mercury-free metal halide lamps.
As a result of the examination, the mercury-free metal halide lamps have significantly different characteristics than those of metal halide lamps containing mercury. For example, in a mercury-free metal halide lamp, arc curving can be suppressed by applying a magnetic field to the mercury-metal halide lamp. However, the manner in which a magnetic field is applied and the principle of suppression of curving are very different from those for the metal halide lamp containing mercury. Furthermore, depending on the intensity of the magnetic field, the arc 7 itself is unstable and a phenomenon that the arc 7 vibrates was observed. This vibration of the arc 7 is not preferable because it results in a flickering when used as a lamp.
Therefore, with the foregoing in mind, it is a main object of the present invention to provide a mercury-free high-intensity discharge lamp operating apparatus and a mercury-free metal halide lamp in which arc vibration is suppressed and flickering is prevented.
A mercury-free high-intensity discharge lamp operating apparatus of the present invention includes a horizontally operated high-intensity discharge lamp including an arc tube in which a luminous material is enclosed and a pair of electrodes are arranged in the arc tube; a ballast including an alternating current generation means for supplying alternating current to the pair of electrodes; and a magnetic field application means for applying in substantially vertical direction a magnetic field having a component that is substantially perpendicular to a straight line connecting heads of the pair of electrodes; wherein mercury is not included as the luminous material in the arc tube; and the present invention satisfies the relationship
0 less than (100BW/f)xe2x88x92P0d less than 100 
wherein B(mT) is the magnetic field applied to a center between the heads of the pair of electrodes, d(mm) is a distance between the heads of the pair of electrodes, P0(MPa) is a pressure inside the arc tube during steady-state operation, W(W) is a power consumed during steady-state operation, and f(Hz) is a steady-state frequency during steady-state operation.
A mercury-free high-intensity discharge lamp operating apparatus of the present invention includes a horizontally operated high-intensity discharge lamp including an arc tube in which a luminous material is enclosed and a pair of electrodes are arranged in the arc tube; a ballast including an alternating current generation means for supplying alternating current to the pair of electrodes; and a magnetic field application means for applying in substantially vertical direction a magnetic field having a component that is substantially perpendicular to a straight line connecting the heads of said pair of electrodes; wherein mercury is not included as the luminous material in the arc tube, and at least a rare gas is included in the arc tube; and the present invention satisfies the relationship
0 less than (10BW/f)xe2x88x92Pd less than 10 
wherein B(mT) is the magnetic field applied to a center between the heads of the pair of electrodes, d(mm) is a distance between the heads of the pair of electrodes, P(MPa) is a pressure of the enclosed rare gas at 20xc2x0 C., W(W) is a power consumed during steady-state operation, and f(Hz) is a steady-state frequency during steady-state operation.
It is preferable that the pressure P of the enclosed rare gas is in the range of 0.1 (MPa) less than P less than 2.5 (MPa).
It is preferable that the pressure P and the distance d satisfy the relationship Pxc2x7d less than 8.
It is preferable that the pressure P and the distance d satisfy the relationship Pdxe2x89xa64.6.
It is preferable that the operating frequency f during steady-state operation is in the range of 40 (Hz) less than f.
It is preferable that the magnetic field B is in the range of B less than 500 (mT).
It is preferable that the distance d between the heads of the electrodes is in the range of 2 less than d(mm).
It is preferable that the high-intensity discharge lamp is a metal halide lamp including at least indium halide as the luminous material in the arc tube.
In one embodiment, the present invention further includes a reflecting mirror for reflecting light emitted by the high-intensity discharge lamp; wherein a center of an arc of the mercury-free high-intensity discharge lamp is arranged on an optical axis of the reflecting mirror.
A mercury-free metal halide lamp of the present invention includes an arc tube in which a luminous material is enclosed and a pair of electrode are arranged in the arc tube; wherein at least an indium halide serving as the luminous material and a rare gas are contained in the arc tube; and mercury is not included as the luminous material in the arc tube; and the present invention satisfies Pdxe2x89xa64.6, wherein d(mm) is a distance between the heads of the pair of electrodes, and P(MPa) is a pressure of the enclosed rare gas at room temperature.
It is preferable that the pressure P of the enclosed rare gas is at least 0.3 (MPa) at room temperature.
It is preferable that the distance d is at least 2 (mm).
In one embodiment of the present invention, the metal halide lamp is operated in a perpendicular direction.
In one embodiment of the present invention, the metal halide lamp is operated in a horizontal direction; and the present invention further includes a magnetic field application means for applying a magnetic field having a component that is substantially perpendicular to a straight line connecting the heads of the pair of electrodes, thereby suppressing arc curving.
In one embodiment of the present invention, the metal halide lamp is of an alternating current lighting type where an alternating current is supplied to the pair of electrodes.
In one embodiment of the present invention, a scandium halide, a sodium halide, and a thallium halide are contained as the luminous material in the arc tube.
In one embodiment of the present invention, a halogen constituting the halides is at least one selected from the group consisting of iodine and bromine.
In one embodiment of the present invention, the rare gas is Xe (xenon).
In one embodiment of the present invention, the mercury-free metal halide lamp further includes a reflecting mirror for reflecting light emitted by the metal halide lamp; wherein a center of an arc of the mercury-free metal halide lamp is arranged on an optical axis of the reflecting mirror.
In the mercury-free high-intensity discharge lamp of the present invention, the relationship of the equation 0 less than (10BW/f)xe2x88x92P0d less than 100 is satisfied, wherein B(mT) is the magnetic field applied to the center between the heads of the pair of electrodes, d(mm) is the distance between the heads of the pair of electrodes, P0(MPa) is the pressure inside the arc tube during steady-state operation, W(W) is the power consumed during steady-state operation, and f(Hz) is the steady-state frequency during steady-state operation, or the relationship of the equation 0 less than (10BW/f)xe2x88x92Pd less than 10 is satisfied, where P (MPa) is the pressure of the enclosed rare gas at 20xc2x0 C. Thus, arc vibrations are suppressed, and flickering can be prevented.
Furthermore, the arc is not in contact with the tube wall, so that the lifetime characteristics can be excellent. More specifically, in the case where a value of {(100BW/f) P0d} or a value of {(10BW/f)xe2x88x92Pxc2x7d} is 0 or less, the arc curves so as to be along the tube wall, and therefore the temperature in the upper portion of the arc tube is increased, and devitrification or deformations occur in the arc tube of the mercury-free high-intensity discharge lamp operating apparatus. As a result, the lifetime characteristics are degraded. The present invention allows such degradation of the lifetime characteristics to be prevented.
When a value of Pxc2x7d is less than 8, an effect of reducing the start-up voltage can be obtained. More specifically, when a value of Pxc2x7d is 8 or more, the start-up voltage may exceed 30 kv. A driving circuit that can generate a start-up voltage exceeding 30 kV can be large-scale. Therefore, it is preferable that the value of Pxc2x7d is below 8. Furthermore, when a value of Pxc2x7d is less than 6, the start-up voltage can be 25 kV or less. As the driving circuit, a circuit that is started with a start-up voltage of 25 kV or less is preferable because it can be smaller. Therefore, by setting the value of Pxc2x7d at 6 or less, an effect of downsizing the circuit can be obtained. It is more preferable that the value of Pxc2x7d is 4.6 or less.
When the pressure P of the enclosed gas at 20xc2x0 C. is 0.1 MPa or more, an effect of improving the stability of the arc can be obtained. When the P is 0.3 MPa or more, an effect of maintaining the stability of the arc can be obtained even when no enclosed material evaporates immediately after turned on. Furthermore, when P is 0.5 Mpa or more, it is possible to facilitate thermal conduction in the arc tube, so that the time required until the temperature in the arc tube is stabilized can be reduced. Thus, the time required until the enclosed material evaporates can be reduced, so that the time required until the mercury-free high-intensity discharge lamp operating apparatus is stabilized can be shortened.
When the P is 2.5 MPa or less, an effect of effectively preventing the breakage of the arc tube can be obtained. More specifically, when the P exceeds 2.5 MPa, the pressure P0 in the arc tube during operation exceeds 25 MPa, so that the arc tube can be broken more easily. Therefore, it is preferable that the P is 2.5 or less.
When P is 2.0 MPa or less, an effect of reducing the start-up voltage can be obtained. More specifically, when P exceeds 2.0 MPa, the start-up voltage at the start of operation exceeds 30 kV. The driving circuit of the mercury-free high-intensity discharge lamp that generates the start-up voltage exceeding 30 kV can be large-scale. Therefore, it is preferable that the P is 2.0 or less also in view of downsizing of the apparatus. In addition, when the start-up voltage of 30 kV or more is applied, the start-up voltage itself can be generated as large noise, thus affecting peripheral equipment. Moreover, higher insulation is required than that of an insulating material constituting the mercury-free high-intensity discharge lamp operating apparatus, which is disadvantageous in terms of the cost. Therefore, it is preferable that the P is 2.0 or less.
When the operating frequency f exceeds 40 Hz, the lifetime characteristics can be improved more effectively. When the operating frequency f is 40 Hz or less, the time during which electrons collide with an electrode on one side during polarity reversal is prolonged, so that the temperature in the heads of the electrodes is increased, so that depletion of the electrodes is facilitated.
When the magnetic field B is less than 500 mT, an effect of reducing the influence of noise with respect to lead lines and peripheral electrical equipment can be obtained. More specifically, When a magnetic field is applied to the arc, the magnetic field occurs not only in the arc, but also in the periphery. On the other hand, when the magnetic field B applied to the center of the electrodes during steady-state operation is 500 mT or more, the magnetic field applied to the periphery is increased. Therefore, noise occurs with respect to lead lines and peripheral electrical equipment, and as a result, malfunctioning can occur. Therefore, it is preferable that the magnetic field B is less than 500 mT.
When the distance d between the electrode heads exceeds 2 mm, the depletion of the electrodes can be prevented, and thus the lifetime characteristics can be improved more effectively. More specifically, when the distance d between the electrode heads is 2 mm or less, it is difficult in the mercury-free metal halide lamp not containing mercury to obtain a suitable lamp voltage (e.g., 60V or more). Therefore, the current value of the lamp is increased, and the depletion of the electrodes is facilitated. For this reason, it is preferable that the distance between the electrode heads exceeds 2 mm. Considering the manufacturing variations, it is more preferable that the distance is 3 mm or more to obtain 60V or more stably.
Furthermore, when a reflecting mirror is further provided and the center of the arc is arranged on the optical axis of the reflecting mirror, light from the arc can be projected effectively. As a result, a mercury-free high-intensity discharge lamp having good efficiency can be obtained. Furthermore, with this configuration, it is possible to realize a high-intensity discharge lamp with a controllable arc position in a simple manner.
According to a mercury-free metal halide lamp of the present invention, Pd is set to Pdxe2x89xa64.6, wherein d(mm) is the distance between the heads of the pair of electrodes and P(MPa) is the pressure of the enclosed rare gas at room temperature. Thus, the present invention makes it possible to suppress arc vibrations and prevent flickering. In other words, flickering during operation of a mercury-free meal halide lamp can be eliminated and stable arc can be obtained.
According to the present invention, the equation 0 less than (10BW/f)xe2x88x92P0d less than 100 is satisfied, wherein B(mT) is the magnetic field applied to the center between the heads of the pair of electrodes, d(mm) is the distance between the heads of the pair of electrodes, P0(MPa) is the pressure inside the arc tube during steady-state operation, W(W) is the power consumed during steady-state operation, and f(Hz) is the steady-state frequency during steady-state operation. Thus, the present invention makes it possible to provide a mercury-free high-intensity discharge lamp in which arc vibrations are suppressed and flickering is prevented.
Furthermore, according to a mercury-free metal halide lamp of the present invention, Pd is set to Pdxe2x89xa64.6, wherein d(mm) is the distance between the heads of the pair of electrodes and P(MPa) is the pressure of the enclosed rare gas at room temperature. Thus, the present invention makes it possible to suppress arc vibrations and prevent flickering.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.